1. Field of the Invention
The invention relates to a method and device for electrolytic treatment of electrically mutually insulated, electrically conductive structures on surfaces of electrically insulating foil material and applications of the method.
2. Description of the Related Art
Electroplating processes among others are used for metal coating of strips. For quite a number of years, so-called reel-to-reel treatment units have been used for this purpose, the material being transported through said units and, during transportation, coming into contact with treatment fluid.
A method for electrolytic etching of aluminium foil is described in U.S. Pat. No. 3,779,877 in which the foil is firstly guided over anodically polarised contact shoes and then guided into the electroplating treatment baths. In the treatment baths, the foil is guided past cathodically polarised electrodes and then taken out of the bath again. The foil is thereby guided once again over anodically polarised contact shoes.
Another method for treating metal strips, metal wires or metal profiles is described in EP 0 518 850 A1 in which method the electrically conductive item to be treated is guided through two containers filled with aqueous electrolytes one after the other for electrolytic pickling, an anodic treatment in the second container following a cathodic treatment in the first container. Current from an electrode in the first container is directed thereby over the item to an electrode in the second container so that, by means of the item to be treated, a circuit is completed between the electrodes of a different polarity, said electrodes being located in the successive containers. In alternative embodiments, oppositely polarised electrodes can also be provided in one treatment container and further electrodes in additional containers.
Furthermore, a method is known from EP 0 093 681 B1 for continuous coating of wires, tubes and other semi-finished products made of aluminium with nickel. In this method, the semi-finished product is firstly conveyed into a first bath container and then into a second bath container. In the first bath container, the semi-finished product is guided past a negatively polarised electrode and, in the second bath container, guided past a positively polarised electrode. A metallising bath is situated in the bath containers. As a consequence of the fact that the semi-finished product is electrically conductive and, at the same time, is in contact with both metallising baths, the circuit between the electrodes, which are connected by a current source, is completed. In contrast to the negatively polarised electrode in the first bath container, the semi-finished product is anodically polarised. In contrast to the positively polarised electrode in the second bath container, the semi-finished product is on the other hand cathodically polarised so that metal can be deposited there.
A method is known from EP 0 395 542 A1 for continuous coating of a substrate, which is made of graphite, aluminium or its alloys, with a metal, the substrate being guided successively through two containers, which are connected to each other and contain an activation bath or a metallising bath, a cathode being disposed in the first container and an anode in the second container. Using this method, rods, tubes, wires, strips and other semi-finished products can be coated as substrates.
A fundamental disadvantage of the above-mentioned methods resides in the fact that only whole-surface conductive surfaces can be electrolytically treated but not electrically mutually insulated structures.
As a solution to the latter problem, a method has been proposed in WO 97/37062 A1 for electrochemical treatment of electrically mutually insulated regions on printed circuit boards. Accordingly, the printed circuit boards, which are brought in contact with the treatment solution, are brought in contact successively with stationary brush electrodes, which are supplied from a current source so that an electrical potential can be applied to the individual electrically conductive structures. An electrical potential is applied between the brushes, which are preferably formed of metal wires, and the anodes, which are disposed between the brushes.
This device has the disadvantage that the brushes are completely covered with metal within a very short time since approximately 90% of the metal is deposited on the brushes and only 10% on the regions to be metallised. Therefore, the brushes must be freed again of metal after just a short operational time. For this purpose, the brushes must be dismantled again from the device and be freed of metal or else elaborately constructed devices need to be provided which help to remove again the metal on the brushes by means of electrochemical polarity reversal of the brushes to be regenerated. In addition, the brush ends can easily damage fine structures on the printed circuit boards. Likewise, the brush material thereby wears quickly, the finest particles being rubbed off and getting into the bath where they lead to damage during metallisation. Especially for metallising very small structures, for example those with a width or length of 0.1 mm, there must be used brushes with very thin wires. These wear especially quickly. Particles which come from the worn brushes then proceed into the bath and into the holes of conductive foil and produce significant defects.
In other known methods for metallising electrically insulated structures, currentless metallising processes are used. However, these methods are slow, difficult to implement and expensive since fairly large quantities of chemical substances are used. The used substances are frequently environmentally damaging and therefore incur further significant costs in disposing thereof. In addition, it is not ensured that only the electrically conductive structures are metallised. It is often observed that, in this case, the metal is also deposited on the electrically insulating surface regions which lie between, resulting in rejection.
A method is described in EP 0 838 542 A1 for electrolytic pickling of metallic strips, especially high quality steel strips, strips made of titanium, aluminium or nickel, the electrical current being directed through the bath without electrically conducting contact between the strip and the electrodes. The electrodes are disposed opposite the strip and polarised cathodically or anodically. It has emerged though that, in the implementation of this method, the current yield in an electrolytic treatment is very small.
Finally, a device is disclosed in Patent Abstracts of Japan C-315, Nov. 20, 1985, Vol. 9, No. 293, JP 60-135600 A for electrolytic treatment of a steel strip. The strip is guided through an electrolytic bath for this purpose between oppositely polarised electrodes. In order to prevent an electrical current flow between the oppositely situated and oppositely polarised electrodes, shielding plates are provided between the electrodes in the plane in which the bath is guided.
The problem underlying the present invention is therefore to avoid the disadvantages of the known electrolytic treatment methods and in particular to find a device and method with which a continuous electrolytic treatment of small electrically mutually insulated, electrically conductive structures on surfaces of electrically insulating foil material is possible at low cost, it also requiring to be ensured that the equipment costs are low and that the method can be implemented with adequate efficiency. In particular, the method and the device should be able to be used for the production of conductive foils in printed circuit board technology.